Process for the preparation of ditolylethane



7atented Mar. 14, 1950 "k' UNITED STATES PATENT "OFFICE PROCESS=FOR THE PREPARATION OF DITOLYLETHANE James A. McCoubrey, Shawinigan Falls, Quebec,

and Frederick Pettit Lossing; Hamilton, nt'ario; Canada, assignors to Shawinigan Chemicals Limi-ted,Montreal, Quebec, Canada, a cor- .poration. of Canada No Drawing." Application September 12,1947, SerialNo. 773,726

8 Claims. (01. 260-668) 1 2 This invention relates to improvements in a the reaction between paraldehyde and toluene method of preparing 1,1 di-p-tolylethane. with the aid of much smaller amounts of 1- Prim." art furic acid than have heretofore been considered necessary. Other objects and advantages of the 1,1 di-1Jt0 1y1ethane, herein referred to asinvention will be apparent from the following detolylethane', has commonly been prep the scr pt onreaction-of acetylene with toluene, in the'pres- Detailed description ence of a catalystsuch as? a'mixture of sulfuric U v 7 acid and mercuric sulfate. The product yields Accordmb thls mventlon, vthe action be- V tween paraldehyde and toluene is carried 0 t b obtainable by this process have been of the m 11 y Z???311111 3iifii ilii y tiiii ifiiiii strength, the paraldehyde ra l commit; Fischer (Ber. '1, 119341874 outlinedamethod 233E 3 fg; a The r of of preparing dimethylphenylethane (ditolyleth- 1 gg gf i i fi i t P aneil,bythereactionorparaldehyde-withtoluene. 1v constant b g t urlsmam m fall Asoutlinediby Fischer;,.the.method requiresthe- {chime is ag -1% e use of -excessively large amounts'of sulfuric acid Standing after c-gn 1 t e react on ixture, on which arelnotirecovered. The yields obtamedby two layewa gg i zh gggi g .55: 1: 28 ggg g 5; fig g ggizhi ig g g igz ditolylethane and anacid layer of sulfuric acid heretofore produced better yields than: any other and water The hydrocarbon layer is Separated process for the preparation: ditolmethana by decantation, and the ditolylethane is recovered e paraldehy e' an to uene was carrie ou y '25 adding a stoichiometric amount ofltoluene to-a hydrocarbon'mlxture 15 recycled to react Wlth mixture of paraldehyde and sulfuric acid, conf h palfaldehyde- The process ma be 0D- taimng not more than 1 1/2% para1dehyde Thus e1 atedas either a batch or continuous process.

for each mole of ditolylethanei there-wereremost crlticalhfactor aficimg the meld of quired nearly 30' moles of:sulfuric acid. 30 ditolylethaine thls process 15 the Strength of the sulfuric acid used. vDuring the reaction the The'mventzon sulfuric acid is diluted by the water which is We have discovered certain improvements formed' Hence the strength Of acid Conwhich make it possible to obtain hitherto untmumlsly decreasing reaction p oceeds.

obtainable yields'of ditolylethane. Our invention Tolnaiintain a s rengthof acid which is coninvolves the reaction between 'paralde'hyde and dual/8'30 the hlghest d'of iolyle hane, it is toluene, the dehydratio being obtained by th necessary either to fortify the acid during the remaintenance of certain critical dehydrating'conaction y addition of oleum, or to start with a, ditions quantity of acid sufficiently large that its strength We have found that by using toluene'in excess 40 Will b pp iably decreased by the Water and sulfuric acid of certain critical strength in formed dllrlng the t on- We have found that an altered addition procedure, the amount of acid Sulfuric acid of about t0 Strength s required to complete the reaction is greatly remost-conducive to high yields Of ditolylethane by duced, and greatly improved 1 of dito1y1 this reaction. (By90% strength sulfuric acid is ethane are obtained. We have also found that mf miXture containing 90 parts y We the yield of ditolylethane is improved according 0f H2304 and p s y Weight of Water.) Acid to our procedure by maintenance of certain. spe- Strengths belOW about do not D B Sat scific'conditions of reaction, such as temperature, factory yields? acid strengths of or lower rate of addition of reactants; ratio of ingredients, Promote desirable reactionv w ever beand agitation o ingredients; m tween paraldehyde and toluene. Acid strengths i above about 93% cause excess formation of tarry Omects lay-products during the reaction, and are unde- It is therefore an'object of this inventionito sirable'for that reason.

produce ditolylethane in high yields by the" re- Dilution: of the sulfuric" acid with inert maaction between paraldehyde and toluene. f It is terials suchas-tar, occurring during this process, a further object ofwthis' invention-to carryout apparentlyadoes not-affect thejffdehydrating strength of the acid. Thus a quantity of acid containing 81 parts H2804, 9 parts water, and 10 parts inert diluent has approximately the same dehydrating strength as acid containing 90 parts H2304 and 10 parts water. It is the dehydrating strength of the acid which should be kept within the range of 87% to 93% in the process of our invention.

During the operation of the process of our invention, we prefer to maintain the temperature of the reaction below 10 .C., preferably below about 5 C. Temperatures about 0 C. are found to give maximum yields and hence are most desirable for this reaction.

The excess toluene used in the process may vary from upwards. of about 35% to 50% is used. No'significant increase in the yields of ditolylethane is obtained with amounts of toluene greater than 50% excess. In batch operation the paraldehyde is added to the toluene, so that the toluene is always present in excess during the reaction. The effects of using excess toluene are illustrated by the following figures.

A series of batches of ditolylethane was prepared by this process using 4%, 44%, and 188% excess toluene in the preparation of the various batches respectively. The yields of ditolylethane obtained, based on the amount of toluene consumed in each case, were 80%, 89%, and 90% respectively. The excess toluene was recovered and used in the same process in subsequent preparations.

As noted above, the paraldehyde to be added to the mixture of toluene and sulfuric acid is preferably diluted with toluene, thus avoiding local high concentrations of paraldehyde in the reaction mixture and ensuring a smooth, evenreaction, 'The fraction of the total amountof toluene mixed with paraldehyde for addition'to the mixture of toluene and sulfuric acid is apparently not critical, but usually comprises from about 5% to about of the toluene used.

The amount of acid in the sulfuric acid-toluene mixture, as previously stated, should be sufficient- 1y large that its strength is not decreased below the preferred range of acid-strength by water formed during reaction. A ratio of about 15 moles of sulfuric acid per mole of toluene in the toluene-acid mixture has been found to be adequate, where the total amount of toluene used was 40% in excess of that required for complete reaction with the paraldehyde and 14% of the toluene was added with the paraldehyde. Thus it is seen that only about four moles of sulfuric acid are required for dehydration for each mole of ditolylethane produced. This is a marked contrast with the thirty moles of sulfuric acid per mole of ditolylethane required by Fischer.

The rate of addition of paraldehyde to the mixture of sulfuric acid and toluene, according to this invention, may be as rapid as the cooling capacity of the system permits, it being required only that the temperature of the system be maintained within the range previously indicated for maximum yields. Good agitation, such as is obtained with a propellor agitator or a turbo mixer, is required for high yields. Poor agitation and consequent poor dehydration conditions may result in yields as low as 15% due to the formation of large amounts of tarry Icy-products. Effective mixing, as required for obtaining the high yields possible by this process, is not diiiicult to obtain.

A typical batch preparation of ditolylethane Preferably, an excess og'eneous' mixture of sulfuric acid and toluene while stirring vigorously and maintaining the temperature of the reacting mixture at about 0 C.

by external cooling.

The resulting hydrocarbon layer was separated by decantation, washed and neutralized, and the ditolylethane was separated therefrom by distillation over a temperature range of C. to C. at a pressure of 1 to 2 mm. of mercury. There were recovered 240 parts of toluene and 403 parts of ditolylethane representing a yield of 84% of theory based on the paraldehyde used and a yield of 96.5% of theory based on the toluene used. H 1

The preparation of ditolylethane from acety lene and toluene with a catalyst of sulfuric acid and mercuric sulfate proceeds through the acetaldehyde stage. By operating the two stages as one process it is not possible simultaneously to Work under the optimum conditions for both stages. By'operating the reaction between aldehyde and toluene as a separate step, as in this invention, it is possible to work under the optimum conditions in both stages of the preparation of ditolylethane from acetylene and toluene. Hence much larger over-all yields may be obtained... ,1.

By the process or this invention, it is possible'to obtain hitherto .unobtain'able: yields of ditolylethane. Furthermore, these high yields of ditolylethane may be obtained withthe use of much less catalyst sulfuric acid than has heretofore been required by this reaction. In addition, the process outlined in this invention is easily controlled and operated, either as a batch or a continuous process, thereby assuring maximum economy.

Throughout the specification, reference has been made to the paraldehyde polymeric form of acetaldehyde as an ingredient in the process of the invention. Monomeric acetaldehyde may be used in place of paraldehyde, but its use is objectionable because of the large amounts of heat liberated when it polymerizes to paraldehyde under theacid conditions of the reaction.

We claim:

1. In aprocess for the preparation of 1, dip-tolylethane, the step of adding to a mixture of toluene and sulfuric acid of 87% to 93% strength, a mixture of toluene and paraldehyde, while maintaining the temperature of the combined mixtures below 10 C., the total amount of toluene in the mixtures being more than 25% in excess of that theoretically required for reaction with the paraldehyde, the amount of sulfuric acid being such that its strength is not decreased below about 87% by the water formed during the reaction.

tolylethane, the step of adding paraldehyde to a mixture of toluene and sulfuric acid of 87% to 93% strength while maintaining the temperature of the combined mixtures below C., the amount of toluene being more than in excess of that theoretically required for reaction with the paraldehyde, the amount of sulfuric acid being such that its strength is not decreased below 87% by the water formed during the reaction) 5. In a process for the preparation of 1,1 di-ptolylethane, the step as in claim 4, in which the amount of toluene is from to in excess of that theoretically required for reaction with the paraldehyde.

6. In a process for the preparation of 1,1 di-ptolylethane, the step as in claim 5, in which the temperature is maintained between 0 C. and 10 C.

7. A process of preparing 1,1 di-p-tolylethane comprising adding to a mixture of toluene and sulfuric acid, a mixture of additional toluene and paraldehyde, with vigorous stirring while maintaining the temperature of the combined mixtures below 10 C, the strength of the sulfuric acid the toluene for further reaction with paraldehyde' in the presence of sulfuric acid.

JAMES A. MCCOUBREY. FREDERICK P. LOSSING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Sturrock et al. Apr. 6, 1948 OTHER REFERENCES Fischer, 0. Berichte, vol. '7 (1874), 1193-4 (2 pages).

Number 

1. IN A PROCESS FOR THE PREPARATION OF 1,1 DIP-TOLYLETHANE, THE STEP OF ADDING TO A MIXTURE OF TOLUENE AND SULFURIC ACID OF 87% TO 93% STRENGTH, A MIXTURE OF TOLUENE AND PARALDEHYDE, WHILE MAINTAINING THE TEMPERATURE OF THE COMBINED MIXTURES BELOW 10*C., THE TOTAL AMOUNT OF TOLUENE IN THE MIXTURES BEING MORE THAN 25% IN EXCESS OF THAT THEORETICALLY REQUIRED FOR REACTION WITH THE PARALDEHYDE, THE AMOUNT OF SULFURIC ACID BEING SUCH THAT ITS STRENGTH IS NOT DECREASED BELOW ABOUT 87% BY THE WATER FORMED DURING THE REACTION. 